A cognitive radio technology is a promising technology for currently solving the problem of low spectrum utilization rate caused by a static spectrum allocation manner. The utilization rate of a licensed frequency band can be effectively increased in a dynamic spectrum access way. Since a primary user in the cognitive radio network has higher priority for spectrum use than secondary users, the secondary users need to detect the signal of the primary user before using a frequency band and to realize coexistence with the primary user by an underlay or overlay spectrum sharing mechanism, so as to avoid generating interference to the communication of the primary user.
The protocol design for network construction of the cognitive radio network is based on that a sender can find a receiver and can use the same channel to communicate. In view of the problem, a channel rendezvous mechanism provides a common transmission medium for the secondary users so as to establish a communication link. This is a necessary process for completing control instruction interaction and data information transmission, and is a precondition for realizing neighbor discovery, handshake between the sender and the receiver, topology control, routing request broadcast, routing information update and other processes.
According to the dependency on a preset dedicated common control channel in the network, the channel rendezvous strategy can be classified into two categories: the auxiliary channel rendezvous strategy and the blind channel rendezvous strategy. The auxiliary channel rendezvous strategy is based on a dedicated common control channel, inherits the idea of protocol design of a traditional multi-channel wireless network MAC (Medium Access Control), and belongs to a static channel rendezvous strategy. Since the preset dedicated common control channel is a channel rendezvous point known by the secondary users, the process of completing channel rendezvous and establishing the communication link for the secondary users can be simplified. However, the network-wide dedicated common control channel can easily become a bottleneck that limits the network capacity due to an increase of network load. The common control channel is easily influenced by the activity of the primary user. When the primary user appears in the control channel, all the secondary users must terminate communication and switch to other channels, causing a decrease of the throughput of the network. Moreover, when the primary user occupies the control channel for long, the access of the secondary users is blocked. Namely, in the cognitive radio network, the common control channel is not always available. In addition, the dedicated common control channel may bring the problem of single-point failure to the network due to a denial of service attack. The blind channel rendezvous strategy is independent of the dedicated common control channel, is a dynamic on-demand channel rendezvous strategy, and is suitable for the property of dynamic change of the channel availability of the cognitive radio network. Further, the blind channel rendezvous strategy can be classified into a channel rendezvous strategy based on signal processing, a channel rendezvous strategy based on the receiver, a channel rendezvous strategy based on a channel hopping sequence, a grouping/clustering-based channel rendezvous strategy and the like. The excellent channel handover property of a cognitive radio device enables the channel hopping manner to become a current major method for achieving the blind channel rendezvous among the secondary users. The channel rendezvous based on the channel hopping sequence is operated on a time slot system. Each secondary user generates an algorithm according to the sequence so as to construct an independent channel hopping sequence. The sequence determines the channel hopping order of the secondary user. Once the sender and the receiver switch to the same channel through channel hopping, the channel becomes a rendezvous channel. The design of the channel hopping sequence comprises a clock synchronization-dependent synchronous sequence and a clock synchronization-independent asynchronous sequence. Apparently, the latter has wider applicability. The coverage range of the channel hopping method is not network-wide, so as to effectively prevent the users from generating the phenomenon of convergent behaviors. To prevent the rendezvous channel from being congested, all the channels of the network shall be ensured to have an equal opportunity to become the rendezvous channel during design, so as to ensure the fairness that the channels are accessed and used. By spreading the rendezvous channels out over all the channels, the feature of channel diversity of the cognitive radio network can be fully used. However, through the adoption of the method, the secondary users need to frequently switch the channels in order to achieve channel rendezvous, causing a large time consumption. To this end, the key is to design the channel hopping sequence for achieving deterministic rendezvous as soon as possible within a finite time.
At present, the rendezvous strategy based on the channel hopping sequence mainly considers that each secondary user only needs to configure one antenna. This is the most common configuration in most of network devices. However, in such network as the cognitive radio network with multiple channels and dynamic change of the channel availability, the delay consumption of rendezvous search is often great. The processing capability of only one antenna is limited, and becomes the bottleneck that restricts the entire performance. Through the use of a multi-antenna cognitive radio device, each antenna independently hops according to respective channel hopping sequences and the feature of the channel diversity can be effectively used. Rendezvous can be achieved as long as any antenna of the receiver and the sender is hopped to the same channel at the same time slot. This channel hopping method for multi-antenna concurrent processing is an effective way for increasing the search efficiency.